Insurance (Obligations Under Funding Agreements - Narrative) (Details) (USD $) In Billions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Insurance [Abstract]
Funding agreements issued to certain SPEs	$ 36.7	$ 26.8	$ 24.7
Funding agreements repaid to certain SPEs	31.7	25.1	21.5
Outstanding funding agreements to certain SPEs	$ 30.3	$ 26.0

Amount of funding agreements during current year issued to certain special purpose entities that have issued debt securities for which payment of interest and principal is secured by such funding agreements.

No definition available.

Name:	mlic_FundingAgreementsIssuedToCertainSpecialPurposeEntities
Namespace Prefix:	mlic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration